As the sliding member constituting a bearing, a sliding material has been known in which a porous layer composed of a copper (Cu) series alloy is formed on a metal substrate and resin materials mixing polytetrafluoroethylene (PTFE) and lead (Pb) coats this porous layer.
Such a sliding material in which a sliding layer is formed by the resin materials has excellent slidability but causes large abrasion loss, which is not suitable for usage under a heavy load condition. Since the usage of Pb is being limited, any sliding material free from Pb has been developed.
As the sliding member constituting a bearing, a sliding material in which Cu series alloy is stuck to a metal substrate has been also known. The sliding material in which Cu series alloy is stuck to the metal substrate such as copper plated steel plate and the like has less slidability than that of a sliding material in which a sliding layer is formed by any resin materials but is capable of preventing abrasion. Further, a technology to accelerate a formation of oil film by forming on a surface of the sliding layer any uneven shapes for oil reservoir has been proposed.
However, under a heavy load condition like an oil hydraulic pump called a piston pump, there has been a case when it cannot maintain such uneven shapes so that it cannot maintain desired slidability in usage for a long time.
When increasing a height of the uneven shape, it is possible to avoid any disappearance of the oil reservoir by abrasion but it is difficult to form the uneven shape having a desired height on the surface of the sliding layer formed by the Cu series alloy.
Accordingly, a technology to improve mechanical strength so that the sliding layer composed of the resin materials is not separated from porous layer by the sliding material in which the sliding layer is formed by any resin material and to form an oil reservoir having a desired shape have been known (For example, see Patent Document 1).